The present invention is directed to an apparatus and process for preparing solid beads or shots from a liquid material. More specifically, the present invention is directed to an apparatus for forming solid beads or shots from liquid, such as a metal alloy, which comprises a chamber for containing a molten material and a plate with a plurality of orifices through which the molten material can pass to form droplet, wherein the molten material in the chamber first contacts the top surface of the plate and wherein bottom surface of the plate contains protrusions through which the orifices extend, the length of each protrusion being at least 50 percent of the total length of the orifice passing through the protrusion, wherein the apparatus is of a material selected from the group consisting of silicon carbide and an alloy comprising nickel in an amount of from about 50 to about 70 percent by weight, molybdenum in an amount of from about 11 to about 22 percent by weight, chromium in an amount of from about 11 to about 22 percent by weight, iron in an amount of from 0 to about 10 percent by weight, tungsten in an amount of from 0 to about 10 percent by weight, manganese in an amount of from 0 to about 1 percent by weight, and silicon in an amount of from 0 to about 1 percent by weight. The present invention is also directed to a process for making shots with the apparatus of the present invention.
Processes for preparing solid shots or beads from liquids such as metal alloys are known. Generally, the process comprises pouring the liquid into a dropping pan or shotter at the top of a high shot tower. The bottom of the dropping pan or shotter is perforated and the molten material passes through the perforations and separates from the pan as discrete particles or drops that assume spherical shape, solidify, and fall into water. U.S. Pat. No. 259,120 (Farrell) discloses a kettle for making drop shot. The kettle, preferably of iron, has perforations through its bottom which are countersunk or conically enlarged on the inner or top surface of the kettle bottom to retard the flow of molten material to the perforations. In addition, U.S. Pat. No. 2,287,029 (Dowdell) discloses a method for making lead alloy shot which comprises supplying a molten alloy of 0.5 to 10 percent magnesium and 90 to 99.5 percent lead to the upper surface of a perforated plate for dropping therethrough in an atmosphere of hydrocarbon gas free of water vapor and oxygen. Further, U.S. Pat. No. 2,510,574 (Greenhalgh) discloses a process for forming spherical pellets from a material in the liquid state which comprises the steps of flowing a continuous stream of the liquid material through an aperture, applying to the stream vibration of a frequency determined by the ratio of the velocity of the continuous stream to a divisor of 3.25 to 5.75 times the diameter of the continuous stream to insure separation of the stream into discrete flobules of uniform size, and maintaining the globules separated until they have solidified. Additionally, U.S. Pat. No. 2,268,888 (Mericola) discloses a method and apparatus for forming fused molten chemical materials into solidified droplets or pellets. The process comprises circulating the molten material into, through, and out of a drop forming chamber, withdrawing a lesser portion of the material then that circulated in the form of droplets from the chamber and dropping them on a cooling surface to form solidified pellets, and controlling the temperature and fluidity of that portion of the material instantaneously in the chamber by varying the rate of circulation. The apparatus comprises a chamber for the reception of a body of material and a plurality of tubes extending through the bottom of the chamber, the lower ends of the tubes being externally cone shaped and the upper ends being disposed at an angle to the horizontal.
U.S. Pat. No. 3,274,642 (Cramer) discloses an apparatus for forming solid spherical granules from molten liquid ammonium nitrate. The apparatus comprises a tower equipped at its top with a plurality of stationary quiescent liquid reservoirs, an orifice plate forming the bottom of each of the reservoirs and through which may freely fall streams of liquid ammounium mitrate, a sound producing system, a sound chamber communication with and depending from the lower portion of the plate, means for communicating the sound producing system and the sound chamber, means for impinging sonic vibrations upon the streams, and means for passing upwardly in countercurrent to the streams blasts of cooling gas. In addition, U.S. Pat. No. 1,951,790 (Curran) discloses a method and apparatus for treating asphalt which comprises a receiver, a tubular shell open at the bottom, means for supporting the shell in a substantially vertical position directly above and in spaced relation to the receiver, an annular chamber enclosing the side walls of the shell, means for circulating fluid through the chamber, and means for introducing liquid in a plurality of streams into the upper portion of the shell.
Shotting processes to form beads or shots of selenuim alloys are also known, as disclosed in, for example, U.S. Pat. No. 4,414,179. Shots or beads of selenium alloy are frequently employed in vacuum evaporation processes to prepare electrophotographic imaging members or photoreceptors, as disclosed in, for example, U.S. Pat. No. 4,894,307, U.S. Pat. No. 4,859,411, U.S. Pat. No. 4,842,973, and U.S. Pat. No. 4,822,712, the disclosures of each of which are totally incorporated herein by reference. Typically, since molten selenium is highly reactive, the molten selenium alloy is passed through a shotter of quartz to minimize contamination of the selenium alloy by reaction products of the selenium alloy and the shotter material. Known quartz shotters, however, exhibit several disadvantages. For example, quartz is a fragile material readily subject to breakage. In addition, quartz, while being far less reactive with selenium and selenium alloys then materials typically employed to make shotters, such as stainless steel, can still contaminate selenium alloy passing through a quartz shotter. Quartz contaminants in selenium alloy shots can result in surface defects on photoreceptors prepared by vacuum evaporation of the alloy shots, since the quartz will also be deposited onto the photoreceptor. Further, known shotters employed to prepare beads or shots of selenium or selenium alloys generally must be removed from the system and cleaned after about 0.5 to 6 hours, since operation after that period of time results in formation of beads or shots larger than the desired size.
Accordingly, while known shotting apparatuses and processes are suitable for the intended purposes, a need remains for improved apparatuses and processes for preparing shots or beads from molten materials. In addition,there is a need for improved shotting apparatuses and processes which enable formation of beads or shots of uniform size for long periods of time without the need for cleaning of the shotter. Further, a need exists for improved shotting apparatuses and processes suitable for preparing shots or beads of selenium or selenium alloys. A need also exists for improved shotting apparatuses and processes that form selenium or selenium alloy beads or shots which result in little or no surface defects when the shots or beads are vacuum evaporated to form an electrophotographic photoreceptor.